fix: issue #135 relating watch mode

[AngusFu]

1. fix Get Multiple files are emitting to the same path warning when watch: true  #135
2. expose watchers for flexibility

[codecov]

Codecov Report

Merging #136 into master will increase coverage by 5.29%.
The diff coverage is 92.85%.

@@            Coverage Diff             @@
##           master     #136      +/-   ##
==========================================
+ Coverage   60.16%   65.46%   +5.29%     
==========================================
  Files          12       12              
  Lines         492      498       +6     
  Branches      194      196       +2     
==========================================
+ Hits          296      326      +30     
+ Misses        158      137      -21     
+ Partials       38       35       -3

Impacted Files	Coverage Δ
src/index.js	66.35% <92.85%> (+5.77%)	⬆️
src/babel.js	87.5% <0%> (+4.16%)	⬆️
src/get-config.js	88.88% <0%> (+38.88%)	⬆️

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[egoist]

🎉 This PR is included in version 3.4.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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